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Old 14th August 2011, 10:51 AM   #14901
Previously: Kuei Yang Wang
 
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Jan,

Quote:
Originally Posted by janneman View Post
You do not understand the issue. It is IRRELEVANT what the ear does, as long as the amp reproduces the original source faithfully.
Yet not a single amplifier in the world does that.

And once the amplifier distorts, then:

Quote:
Originally Posted by janneman View Post
To do that, the amp needs low distortion. Low enough so that it is ideally below the threshold of the ear to hear a difference.
The critical point here is: "below the threshold of the ear to hear a difference."

And this threshold varies with SPL, frequency and order of the distortion products, both HD and IMD.

Quote:
Originally Posted by janneman View Post
If the ear can discern a difference between 1% thd and 2% thd than obviously for faithfull reproduction, the amp should distort less than that.
The very fact that you still cite THD shows that the whole argument was not understood. THD is not capable of giving information about distortion audibility.

In fact, it is trivial to construct a system that distorts a signal to give 5% THD at maximum level and which is judged as undistorted by listeners (Geddes for example did so) and it is equally trivial to construct a system that gives 0.01% THD at maximum level and which is judged by listeners as extremely distorted in an objectionable manner (Geddes did something similar).

So low THD does not ensure low audible distortion and high THD does not make for high audible distortion, hence THD is meaningless.

Quote:
Originally Posted by janneman View Post
It is IRRELEVANT that the ear internally distorts 10, 20, 30 or 40%
Again it is highly relevant.

Let's make this crystal clear.

As long as the distortion in the recording and playback system is substantially lower at all harmonics and resulting IMD products and with the correct phase AND of a pattern similar to the ears, it will not be audible...

Ciao T
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Old 14th August 2011, 12:00 PM   #14902
BV is offline BV  Slovakia
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Quote:
The critical point here is: "below the threshold of the ear to hear a difference."
And this You can estimate very simply with diferential test. You believe, You can hear "something" -100dB below actual music signal? What about masking?
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Old 14th August 2011, 01:00 PM   #14903
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Quote:
Originally Posted by BV View Post
And this You can estimate very simply with diferential test. You believe, You can hear "something" -100dB below actual music signal? What about masking?
No.
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Old 14th August 2011, 01:21 PM   #14904
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Quote:
Originally Posted by ThorstenL View Post
Hi,



I know you intended what you wrote to be cynical, but what makes it really funny (I am still holding my side) is that it actually describes reality rather well...

The whole concept of a linear frequency response is a complete illusion, created in "my day" by judicious pen-damping and nowadays by the use of averaging.

If you ever saw the raw, unaveraged frequency response of speakers that are presented as having a flat frequency response, you would be appalled at the fact that they are not even +/-10dB flat.

Another facette is one particular speaker myth that I keep noticing, namely that of the "Baffle Step", which actually produces a 6dB LF Boost in the power response.

Yet most here and many commercial speaker designers use it anyway and insist it must be used, creating what is in effect (and this indeed is the reason for preferring to apply it) a fixed, undefeatable "Loudness" contour to compensate for listening levels that are lower than "realistic".

Ciao T
Thorsten, you really go out on a limb here. This post really shows you don't know your a from your e. Flat frequency response is one of the most important design goals for loudspeakers and has been recognized as such for a long time, at least by the two companies I have been working with. Clear design goals work. Some of the better speakers easily stay in between +/- 2dB nowadays. No averaging, no tricks.

Your wholesale dismissal of baffle step compensation on the notion that this equates to a 6dB LF boost shows a gap in your knowledge. Read up on the subject, please, so that you understand the physics behind it. And look at how it is implemented by knowledgeable companies. 6dB really is the outer limit, usually it is much less. Yet, you often need it to compensate for Mother Nature at work.

What really disappoints me though, and I made this statement before, is that high end speaker manufacturers almost never show the FR of their products, nor do they publish impedence graphs. Incomprehensible for such expensive technical products that can easily measured. You are no exception.

For good measure, please find below the sort of FR, unsmoothed, not averaged, good design can accomplish with average quality components.
zelfb2.jpg
Everything below 400 hz needs to be taken with a grain of salt, they haven't gone out for anaechoïc measurement yet.

vac
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Old 14th August 2011, 01:33 PM   #14905
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Quote:
Originally Posted by ThorstenL View Post
Jan,



As long as the distortion in the recording and playback system is substantially lower at all harmonics and resulting IMD products and with the correct phase AND of a pattern similar to the ears, it will not be audible...

Ciao T
Thorsten,

"A pattern similar to the ears" You should refrain from statements like that if you can't even give a substantial response to my post #14878.

vac
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Old 14th August 2011, 01:53 PM   #14906
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Quote

"So low THD does not ensure low audible distortion and high THD does not make for high audible distortion, hence THD is meaningless."

With all due respect, this is nonsense.


It is right and proper to aspire to a reproduction signal chain that produces ZERO distortion. Once commted to tape, or whatever storage medium you care to name, by the artist and recording engineer, the reporduction signal chain ideally should have NO influence on the signal coming off the source. And,by ZERO distortion, we mean any kind you want to name - IMD, PMD, Transient etc etc. There's a whole community working on this and hoping they can get there one day.

The fact that designers **** this concept up with argumants against feedback, for feedback, for tubes and againt tubes, or use techno babble that the ear can hear -100dB is the sad bit.
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Last edited by Bonsai; 14th August 2011 at 02:05 PM.
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Old 14th August 2011, 02:00 PM   #14907
Pano is offline Pano  United States
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Old 14th August 2011, 02:07 PM   #14908
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Hi,

Quote:
Originally Posted by vacuphile View Post
Flat frequency response is one of the most important design goals for loudspeakers and has been recognized as such for a long time, at least by the two companies I have been working with. Clear design goals work. Some of the better speakers easily stay in between +/- 2dB nowadays. No averaging, no tricks.
I have yet to measure anything like that.

Maybe we use different measurement methods.

In fact, I find it difficult to get results that are sufficiently repeatable with better than +/-1dB (unsmoothed and without averaging) even with a fair bit of attention paid to orientation, microphone positioning etc. using the tools I have.

Quote:
Originally Posted by vacuphile View Post
Your wholesale dismissal of baffle step compensation on the notion that this equates to a 6dB LF boost shows a gap in your knowledge.
I said it produces a 6dB LF boost in the power response of the speaker (which it does). Normal rooms produce a resultant frequency response that is significantly boosted at low frequencies if they have sufficiently stiff walls. This is actually easy to measure as well.

Quote:
Originally Posted by vacuphile View Post
6dB really is the outer limit, usually it is much less. Yet, you often need it to compensate for Mother Nature at work.
So we are back to bending the response of what should be a flat speaker to match what the ear wants to hear?

Quote:
Originally Posted by vacuphile View Post
What really disappoints me though, and I made this statement before, is that high end speaker manufacturers almost never show the FR of their products, nor do they publish impedence graphs. Incomprehensible for such expensive technical products that can easily measured. You are no exception.
First, I personally am not a high end speaker manufacturer, nor do I control any policy of what such a company chooses to release or not.

Secondly, given that even small shifts in microphone position tend to cause substantial changes in frequency response (without smoothing) the whole "frequency response" thing is yet another "how long is a piece of string".

Quote:
Originally Posted by vacuphile View Post
For good measure, please find below the sort of FR, unsmoothed, not averaged, good design can accomplish with average quality components.
Good for you. I never get anything like such results unless I use smoothing, so clearly I am doing something wrong. Could you elaborate on the measurement process that produced these results without?

Ciao T
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Old 14th August 2011, 02:13 PM   #14909
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Quote:
Originally Posted by vacuphile View Post
Some of the better speakers easily stay in between +/- 2dB nowadays. No averaging, no tricks.

For good measure, please find below the sort of FR, unsmoothed, not averaged, good design can accomplish with average quality components.

vac
How many points on your FFT? How many averages? Are you exciting with an oscillator or pink noise?

The old fashioned pen recorders had adjustable damping to smooth the plots. One of Harry Olson's secrets to getting good plots was to set the damping at maximum.

The example you show is not = +/- 2 db and 10 db variation can also be expressed as +/- 5.

Whenever I have looked at a loudspeaker even a single driver requires smoothing to get useful curves. Throwing pink noise at a driver and then looking at many averages to smooth things out gives you much the same effect as turning up the damping. That allows you to see things you can fix, not a forest of trees.

T, we cross posted!
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Old 14th August 2011, 02:16 PM   #14910
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Quote:
Originally Posted by Bonsai View Post
It is right and proper to aspire to a reproduction signal chain that produces ZERO distortion. Once commted to tape, or whatever storage medium you care to name, by the artist and recording engineer, the reporduction signal chain ideally should have NO influence on the signal coming off the source. And,by ZERO distortion, we mean any kind you want to name - IMD, PMD, Transient etc etc. There's a whole community working on this and hoping they can get there one day.
This kind of aspiration is useless, since even a single resistor, as well as any part of the circuit, including isolated wire, produces MEASURABLE distortion.
And you are right, speaking about a need to MINIMIZE a wide spectrum of distortions.
All the boomy reaction of many people in this thread, just caused by the popular practice to play with THD, everywhere, at any corner, at any thread, by using a multitude of simulation tools. An opposite camp just trying to say, stop cheeting less experienced buyers and DIYers, audio reproduction is mainly not a THD, and the big love to THD simply precludes from better understanding of a real situation, that is contradictory and compromised, where improving one parameter one almost enevitably make others worse. The position, all kind of distortion should be nulled, is obviously impossible. Even by increasing a number of stages in the circuit, we inevitably accumulate distortions of passive parts, this is one of the sides of inherent contradictions.

Last edited by VladimirK; 14th August 2011 at 02:24 PM.
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